1. Technical Field
Example embodiments relate to a method of manufacturing a nitride semiconductor substrate.
2. Description of the Related Art
The use of nitride (e.g., gallium nitride (GaN)) semiconductors in the electronics industry is expected to increase because of the beneficial physical and chemical properties of such semiconductors. Unlike a silicon (Si) semiconductor or a gallium arsenide (GaAs) semiconductor, a GaN semiconductor has a direct transition type bandgap structure, wherein the bandgap can be controlled to be 1.9-6.2 eV using an indium (In) or aluminum (Al) alloy. Consequently, a GaN semiconductor has utility as an optical device. Additionally, because GaN has a high breakdown voltage and is stable at high temperatures, it is also useful as a material for various devices (e.g., high output devices, high temperature electronic devices) which have been difficult to realize using conventional materials. Examples of these devices are large-sized electric signs using a full color display, traffic lights, light sources of an optical recording medium, and high output transistors of an automobile engine.
A conventional GaN-based semiconductor device (e.g., nitride semiconductor laser diode) is formed on a c-plane GaN substrate. However, the c-plane is also known as a polar plane, wherein the bonding probability of electrons and holes may be decreased by the influence of an internal electric field generated by polarization. As a result, the luminescence efficiency of a laser diode may be decreased. To solve this problem, in the prior art, a semiconductor device is realized by epitaxially growing an a-plane GaN on an r-plane of sapphire. However, the cost of the r-plane of sapphire is relatively high. Furthermore, because the lattice mismatch between a (1120) plane of the r-plane sapphire substrate and a (1100) plane of the a-plane GaN is about 16.2% (which is relatively high), a defect may be created by the strains in the a-plane GaN layer that is stacked on the r-plane of the sapphire.